1. Field of the Invention
The present invention relates to radio-frequency antennas. More particularly, the present invention relates to multi-element Yagi antennas and to such antennas having electrically-shortened elements.
2. The Prior Art
Yagi antennas are known in the art. A typical prior-art 3-element Yagi antenna is depicted in FIG. 1. The rear element, known as the reflector, is longer than the center driven element. The front element, known as the director, is shorter than the driven element and the reflector.
Electrically-shortened Yagi antennas are known in the art. Electrically shortening the elements allows them to be physically shorter but still resonate at the desired frequency. Among the advantages obtained by shortening the elements is the reduction of the turning radius of the antenna.
Shortened Yagi antennas are useful in applications where the physical size of a full-sized Yagi would not be practical or possible. When a Yagi antenna is constructed exclusively with elements shorter than full length, its performance is degraded. This degradation is directly proportional to the degree of the reduction in physical length. The more the elements are electrically shortened, the more performance is degraded. Because of this, conventional design practice dictates keeping all of the elements as long as possible to preserve performance characteristics.